Beatband Sleeve

Wear your heartbeat on your arm with the Beatband Sleeve. You’ll combine a pulse sensor with a DIY Arduino microcontroller (and a minty tin) to create this wearable pulse-blinking project. Connect the sensor to your body wherever you get a good pulse reading, and display your heartbeat on the five flashing LEDs. Wear it while you run, play video games, or even while you meditate to show your calming heartbeat ryhthm.

This project goes through several iterations of the circuit. First you’ll build a fully functional Arduino on a breadboard using the parts from a MintDuino kit. Then you’ll re-flash that circuit with the program for the Pulse Sensor. Finally you’ll transfer the circuit to perfboard and fit it all inside the tin for a fun, wearable project that slips into a sports armband.

Step #2: Prepare the pulse sensor.

Before you can upload a sketch to the MintDuino, you have to tell the Arduino IDE what kind of Arduino to flash. Select the option at Tools → Board → Arduino Duemilanove w/ ATmega328.

Open the code file A_PulseSensor_06.ino but don't upload it just yet. Let's prepare our Pulse Sensor first. Check out the Getting Started Guide from the Pulse Sensor website. The guide will tell you that in order to protect the electronics on the sensor, you’ll want to place one of the clear stickers on the front of the sensor and put a layer of hot glue (or velcro) on the back.

Step #3: Test the pulse sensor and upload the code.

Plug the Pulse Sensor into your breadboard: connect its red wire into the positive (red) rail on the breadboard; black wire into the negative (black or blue) rail on the breadboard; and purple wire into a row connected to pin 23 on the microcontroller IC (integrated circuit) chip.

Now connect the 9V battery's red wire to the positive rail its black wire to the negative rail. The Pulse Sensor’s bright green LED should light up immediately.

Connect the MintDuino to your computer via USB and the FTDI Friend.

Place the FTDI Friend on the 6-pin header on the breadboard so that the side with the USB port is facing the green LED.

While everything is still connected, click the Upload button in the Arduino IDE. Once the sketch has been successfully uploaded, the green LED on the breadboard will light back up. The green LED on the Pulse Sensor will also light up immediately. If everything is working, we're ready to build our circuit!

Step #4: Transfer the MintDuino to perfboard.

The breadboard MintDuino is a classic project in and of itself, and has been used as the brain of previous Weekend Projects, notably the Repeat After Me game. However, for this build we want to transfer it to perfboard so it'll fit snugly in the mint tin and the armband sleeve.

Follow these instructions to transfer the MintDuino from breadboard to perfboard, with one minor exception: don't solder the green LED to the perfboard. You'll replace this component with jumper wires connecting to your 5 red LEDs on the lid (see Steps 9–13).

Step #7: Solder the pulse sensor's power and ground.

Since the ATmega IC is soldered to the perfboard off-center, the center rails provide us with power and ground throughout the circuit.

Clamp the perfboard in the vise with the IC facing down on the lower third of the board. Solder the Pulse Sensor's positive lead to the top row of the center rails, and solder its negative lead to the bottom row of the center rails.

Step #10: Enlarge the holes for the LEDs.

One benefit to using the MintDuino tin rather than an Altoids tin is that the MintDuino tin has a plastic coating. This coating tends to cover the sharp edges of the holes – which helps keep the holes from tearing the armband’s fabric.

Widen the holes just enough to achieve a snug fit for your LEDs, using needlenose pliers, screwdriver, awl, or whatever tool you have handy.

TIP: Work from the top of the tin. Your goal is to enlarge the holes in such a way that any rough edges will be on the underside of the lid. This helps protect the armband.

Step #11: Mount the LEDs.

Slide the 5 LEDs into their holes from the underside of the lid, orienting them so that all their negative legs are on one side, and positive legs on the other. For example, the third photo here is from later on in the build, but you can see I marked a + and – on the tape to remind me which side was positive and negative.

Step #13: Solder the LEDs.

Bend all the LEDs' positive leads so that they touch each other. Also bend all the negative leads so that they touch each other.

Solder all the positive leads together. I did this by going from right to left, bending each LED in the row so that it could hook over on the next one to it. The illustration shows one way of doing this.

Repeat to solder all negative leads together.

TIP: When soldering the LEDs, be careful to not reheat the hot glue too much or get any on your soldering tip.

Step #15: Insulate the tin and run your wires.

Did you remember to save the cardstock insert for the MintDuino? Great! Place the card in the tin and then place your perfboard on top. You don’t want the circuit to short itself on the tin. The card will reduce the risk.

Pry open one of the tin's hinge holes just enough to run your Pulse Sensor and battery connector through.

If everything goes according to plan, your perfboard will fit inside the tin with plenty of room to play with.

Step #16: Close it up!

Step #17: Put it all together.

Slip the tin into the armband pouch. I highly recommend the NXE ActiveSleeve for this project. Instead of neoprene, it's made of a stretchy material that allows the light from the LEDs to shine through. You don't need to modify the armband at all.

Pull the velcro flap closed over the pocket, leaving the pulse sensor leads running out to the side.

Route the leads for the pulse sensor through the center of the armband. The elastic of the armband will hold the pulse sensor in place against your arm.

Position the sensor against your bicep near the inside of your elbow. The excess leads from the sensor can be bunched up inside the armband, underneath the MintDuino tin.